1. Field of the Invention
The application relates to a method utilized in a wireless communication system, and more particularly, to a method of handling hybrid automatic repeat request acknowledgement responses in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple UEs, and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In the LTE-A system, since the advanced techniques are supported, such as new carrier type, frequency domain inter cell interference coordination (ICIC), spatial reuse of the resources in coordinated CoMP transmission and downlink MIMO, enhanced physical downlink channels (ePDCCHs) are provided to improve the related abilities. An obvious case is the heterogeneous network scenarios, where the ePDCCHs could be coordinated to avoid interference between macro and low power nodes. In a shared cell scenario, spatial reuse for the same enhanced control channel resource and a downlink transmission on a packet downlink shared channel (PDSCH) within the cell is possible, which provides higher spectrum efficiency. In the CoMP, the uplink transmission will also benefit from the cell splitting gains, which will lead to a problem of collisions between physical indicator channels (PHICH). Therefore, it is natural to consider another type control channel, such as enhanced PHICHs (ePHICH), which is able to accompany the ePDCCH to support frequency domain ICIC and spatial reuse within the cell and capable of operating as PHICH operation.
Moreover, when considering the new carrier type which has reduced overhead of legacy of control signaling and cell-specific reference signal (CRS), the use of PHICHs may not be possible. Therefore, the ePHICH design is necessary for the new carrier type and should have the same capacity as the PHICH design.